Early reports have suggested a dramatic decline in some schools' GCSE results, as a raft of measures designed to toughen up the qualification take effect.

Changes to the compulsory English language exam and a move away from modular assessments - placing more pressure on end of summer exams - are among the measures believed to have affected some pupils.

The changes come amid a growing emphasis on outcomes at GCSE level, with changes further down the education system at A-level causing universities to rely more heavily on Year 11 results.

"There is so much pressure on all the exams being all at once that it feels like it is so important," said Will, 16, a pupil at King Edward VI School in Bury St Edmonds.

"If we don't do well this year because of the Gove effect, and then next year ... we are at such a disadvantage compared to the year above us and the year below because their results are going to be so much better than ours", said Siobhan, 16, also a pupil at King Edward VI.

Teachers say they are concerned that the drop in performance by schools, even if caused by systemic change, could lead to heads being forced out of their jobs.

"I think the pressure on head teachers because of results and then because of Ofsted is quite extraordinary," said Geoff Barton, head teacher at King Edward VI.

Image Caption:Michael Gove made a number of reforms during his time as education chief

"I think we will look back and think it's a national scandal that every year some head teachers simply disappear either because they've been quietly sacked or because they've been publicly sacked because of one year's results.

"And I think that would be a disgrace if that were to happen this year when we know about the turbulence in the system."

Video:'Soft' GCSEs & A-Levels To Be Axed

There are also reports that schools are resorting to increasingly desperate measures to protect their league table rankings in the face of a drop in results.

Experts are predicting a rise in the number of appeals against individual grades and say there has been a significant increase in the number of pupils requesting assistance.

Sky News has learned of concern that some schools pressured pupils to drop a subject shortly before their exams, to avoid poor grades affecting the school's academic record.

One official, who did not want to be named, said there was also concern that schools were wrongly entering their pupils as external candidates, removing their performance from the schools' rolls.

But others said the changes would make it harder for schools to cheat the system.

"(Schools) are held to account through their pupils' exam results. and so they tended to find every way that's open to them to actually push up their students results," said Professor Alan Smithers, director of the Centre for Education and Employment Research.

"Those methods of accountability have changed this year ... the Government has been trying to make exams sounder and also make the accountability system smarter, so that exams work to the best advantage of pupils, universities and employers."